Gov. Christie's office ordered the most heavily trafficked bridge in the country (if not the world) closed for political revenge. He is desperately trying to throw his staff under the bus to avoid accountability for this. It's a very delicate subject for him right now, and Musk bringing it up is cruel and yet at the same time (imho) totally fair play.
I love it, personally. Elected officials should be dragged over coals publicly for crap like the bridge closure AND this sneaky legislative practice he used to get the anti-Tesla laws in.
Completely fair play. To me, Musk is just pointing out that Christie is a corrupt bully (who would absolutely play this exact same card if the situations were reversed).
What everyone else said re: Bridgegate (thanks!) + the original line, which is a reference to the conman George C. Parker, who would sell things like the Brooklyn Bridge to unsuspecting tourists, which, according to Wikipedia, gave rise to the line "If you believe that, I've got a bridge I can sell you."
Chris Christie's administration closed 3 lanes of the George Washington Bridge for a bogus "traffic study", making tons of Traffic. It was political payback against the city of Fort Lee who has a mayor who wouldn't endorse Christie when he was running for governor. Christie says he didn't know about it but some in his administration have left or been asked to leave over it.